Read the passage and answer the following questions:
The earthworm is often referred to as the farmer's 'friend' due to its beneficial role in the breakdown of complex organic matter and soil aeration. Similarly, decomposers play a crucial role in converting complex organic matter into inorganic substances like carbon dioxide, water, and nutrients through the process of decomposition. Detritus, consisting of dead plant remains (leaves, bark, flowers) and animal waste, serves as the raw material for decomposition. Decomposition involves several important steps: fragmentation, leaching, catabolism, humification, and mineralisation. Detritivores, like earthworms, contribute to the process by breaking down detritus into smaller particles, which is known as fragmentation. Through leaching, water-soluble inorganic nutrients percolate into the soil horizon and precipitate as less accessible salts. Bacterial and fungal enzymes play a vital role in degrading detritus into simpler inorganic substances, and this process is referred to as catabolism. It's essential to understand that all these steps in decomposition occur simultaneously on the detritus. Humification and mineralisation are significant processes occurring during decomposition in the soil. Humification involves the transformation of organic matter into stable, dark-coloured substances like humus. Mineralisation, on the other hand, refers to the conversion of organic nutrients into inorganic forms that plants can readily absorb.
Two heaps of litter are kept side by side under the same climate. Heap X is rich in lignin and chitin; heap Y is rich in nitrogen and water-soluble substances like sugars. Which of the following is correct?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Heap Y decomposes faster, as decomposition is quicker when detritus is rich in nitrogen and sugars
The rate of decomposition depends on two things: the chemical composition of the detritus and the climate. Here the climate is the same for both heaps, so only the chemical make-up of the litter decides which one breaks down faster.
Option (1) Heap X decomposes faster, as lignin and chitin are readily broken down by soil microbes — Incorrect. Lignin and chitin are not easily broken down. Detritus rich in them decomposes slower.
Option (2) Heap Y decomposes faster, as decomposition is quicker when detritus is rich in nitrogen and sugars — Correct. In the same climate, detritus rich in nitrogen and water-soluble substances like sugars decomposes quicker. So heap Y breaks down faster.
Option (3) Both heaps decompose at the same rate, as the climatic conditions are the same — Incorrect. Climate is only one of the two controlling factors. With the same climate, the heaps still differ in chemical composition, so they do not decompose at the same rate.
Option (4) Heap Y decomposes slower, as its sugars are lost by leaching before catabolism — Incorrect. Leaching moves water-soluble inorganic nutrients down into the soil; it does not make a sugar-rich heap decompose more slowly. Heap Y in fact decomposes faster.
NCERT Extract:
Decomposition – “… Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars.”